The present invention relates generally to automotive service equipment designed to measure imbalance in a vehicle wheel assembly, and in particular, to an improved wheel balancer system configured to adjust an imbalance correction threshold level for wheels mounted to the wheel balancer system.
Wheel balancer systems are designed to determine characteristics of a rotating body such as a wheel assembly consisting of a wheel rim and a pneumatic tire, or of a wheel rim alone. The determined characteristics include, but are not limited to static imbalances (i.e., “shake” forces), dynamic imbalances (i.e., couple or “shimmy” forces), lateral forces, radial forces and runout parameters. Determination of some of these characteristics result from direct measurements, while others are obtained from an analysis of the mechanical vibrations caused by rotational movement of the rotating body. The mechanical vibrations are measured as motions, forces, or pressures by means of transducers mounted in the wheel balancer system, which are configured to convert the mechanical vibrations into electrical signals.
Additionally, it is important to provide an operator with information about whether or not there is a need to correct a detected imbalance in the wheel rim or wheel assembly, or if the detected imbalance is sufficiently small so as to have a negligible effect on vehicle performance and handling. Currently, wheel rim sizes in the U.S. market range from 13.0 inches in diameter up to and including the present DOT limit of 24.0 inches in diameter. It is anticipated that wheel rim sizes will increase to 26.0 inches in diameter in the near future, with a corresponding increase in associated tire sizes. A problem presented by the continued increase in wheel rim and wheel assembly sizes is the effect of a fixed imbalance correction weight threshold level.
Due to the limited size increments in which imbalance correction weights are available, conventional balancer systems are configured to display as zero any required imbalance correction weight values below a threshold. Typically the predetermined threshold is 0.29 oz., and is selected to be slightly greater than the smallest imbalance correction weight increment, regardless of the size of the wheel rim or wheel assembly. This can result in an operator “chasing” weights on a small or narrow wheel due to the significant effect of the threshold level on imbalances, and a poor balance on larger diameter wheels due to a reduced effectiveness of the threshold level. One solution is shown in U.S. Pat. No. 6,484,574 to Douglas, in which a balancer is configured to select the best weight plane locations from data acquired by scanning the rim profile. This is an advantageous method, but it is not economical for all balancers to have this feature.
Clearly, it would be further advantageous to provide a wheel balancer system with a method for determining an imbalance threshold level which is independent of the dimensions of the wheel assembly undergoing balancing or the incremental size of the imbalance correction weight employed, and which optionally provides an operator with a scaled visual indication of any imbalances present relative to the determined imbalance threshold level.